Abstract
BackgroundThe impact of anesthetic equipment on clinical practice parameters associated with development of acute respiratory distress syndrome (ARDS) has not been extensively studied. We hypothesized a change in anesthesia machines would be associated with parameters associated with lower rates of ARDS.MethodsWe performed a retrospective cohort study on a subset of data used to evaluate intraoperative ventilation. Patients included adults receiving a non-cardiac, non-thoracic, non-transplant, non-trauma, general anesthetic between 2/1/05, and 3/31/09 at the University of Michigan. Existing anesthesia machines (Narkomed IIb, Drager) were exchanged for new equipment (Aisys, General Electric). The initial subset compared the characteristics of patients anesthetized between 12/1/06 and 1/31/07 (pre) with those between 4/1/07 and 5/30/07 (post). An extended subset examined cases two years pre and post exchange. Using the standard predicted body weight (PBW), we calculated and compared the tidal volume (total Vt and mL/kg PBW) as well as positive end-expiratory pressure (PEEP), peak inspiratory pressure (PIP), Delta P (PIP-PEEP), and FiO2.ResultsA total of 1,414 patients were included in the 2-month pre group and 1,635 patients included in the post group. Comparison of ventilation characteristics found statistically significant differences in median (pre v post): PIP (26 ± 6 v 21 ± 6 cmH2O,p < .001), Delta P (24 ± 6 v 19 ± 6 cmH2O, p < .001), Vt (588 ± 139 v 562 ± 121 ml, p < 0.001; 9.3 ± 2.2 v 9.0 ± 1.9 ml/kg predicted body weight, p < .001), FiO2 (0.57 ± 0.17 v 0.52 ± 0.18, p < .001). Groups did not differ in age, ASA category, PBW, or BMI. The two year subgroup had similar parameters. Risk adjustment resulted in minimal differences in the analysis. New anesthesia machines were associated with a non-statistically significant reduction in postoperative ARDS.ConclusionsIn this study, a change in ventilator management was associated with an anesthesia machine exchange. The smaller Vt and lower PIP noted in the post group may imply a lower risk of volutrauma and barotrauma, which may be significant in at-risk populations. However, there was not a statistically significant reduction in the incidence of post-operative ARDS.
Highlights
The impact of anesthetic equipment on clinical practice parameters associated with development of acute respiratory distress syndrome (ARDS) has not been extensively studied
The intraoperative use of low tidal volumes has been associated with faster extubation and less reintubation in patients, while larger tidal volumes are associated with increased risk of postoperative organ dysfunction after cardiac surgery [3,4]
Differences were found in the intraoperative use of colloids, the amount of crystalloid administered, and multiple ventilatory parameters. These included a substantial reduction in the peak inspiratory pressure, a decrease in the amount of positive end-expiratory pressure (PEEP), a decrease in the median Tital volume (Vt), and a decrease in the median drive pressure (Figure 1)
Summary
The impact of anesthetic equipment on clinical practice parameters associated with development of acute respiratory distress syndrome (ARDS) has not been extensively studied. Anesthesiologists typically used mechanically-set volume-cycled ventilators to support patients intraoperatively These ventilators allowed anesthesiologists to set the tidal volume and either the driving pressure or the inspiratory time (sometimes through manipulation of the respiratory rate and I:E ratio.) the actual volume delivered would vary based on breathing circuit compliance, chest compliance, and fresh gas flow. Newer microprocessor-controlled ventilators with automatic compensation for tube compliance and varying fresh gas flow have been shown to be more accurate at delivering small tidal volumes under conditions of both normal and low lung compliance [10]. They allow the user more control over respiratory parameters
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